Process for producing bulkable filamentary polyamide yarns



United States Patent 3,107,972 PROCESS FOR PRODUCING BULKABLE-FILAMENTARY PGLYAMIDE YARNS Giibert Pitzl, Chattanooga, Tenn., assignorto E. I. du

Pont de Nemours and Company, Wilmington, Del, a

corporation of Delaware No Drawing. Filed Oct. 24, 1962, Ser. No.232,877

8 Claims. (Cl. 1854) invention relates generally to the production offilamentary nylon yarn and, more particularly, to an improved processfor preparing continuous filament yarns having the property of becomingbulky upon appropriate heat treatment.

It is well known that yarns from staple fibers, particularly fromnatural fibers such as cotton and Wool, are more voluminous or bulky incharacter than are continuous filament yarns and that such bulkinessleads to fabrics which have high covering power and a soft hand. Variousbulking procedures have been attempted in the continuing effort tocombine the desirable aesthetic properties of fabrics prepared fromstaple yarn with the advantages of continuous filament yarn, such asstrength and ease of processing.

It is also known that bulky continuous filament yarns have been preparedfrom filaments which shrink differentiaily upon treatment with water orheat. One process which has been employed to accomplish differentialshrinkage is to extrude filaments of different deniers from the samespinneret. As disclosed in US. 2,980,492, polyester filaments ofdifferent denier shrink to a considerably different extent when heatedand a desirably bulky yarn is produced. However, when the patentedprocedure is applied to polyamide yarn, very little difference inshrinkage is observed.

It is accordingly the most important object of this in vention toprovide a process for producing bulkable, filamentary, polyamide yarns.Another objective is to provide a process for producing a continuousfilament polyamide yarn containing filaments of the same composition butdifferent deniers, the higher denier filaments having the capability ofshrinking to a significantly greater extent than the lower denierfilaments.

The above objects are accomplished by extruding and quenching aplurality of low and relatively high denier polyamide filaments,arranging the quenched filaments to avoid cont-act between low and highdenier filaments and gathering the filaments, after an axial advancefrom the point of arrangement through a distance sufficient to developsubstantially maximum undrawn orientation, into a yarn bundle adapted tobe drawn. Preferably, the drawingstep is carried out in free space, withno frictional contact between the yarn and solid surfaces, whilesimultaneously heating the yarn end in the draw zone with a jet ofsteam. Alternately, the yarn end may be pin drawn in the conventionalmanner and subsequently heated with steam in a controlled relaxationstep. To insure sufficient shrinkage differential, the average drawndenier of the low denier filaments should be no greater than 2 and theaverage drawn denier of the relatively high denier filaments should beat least 1.5 times that of the low denier filaments. If the undrawn yarnis packaged before drawing, the filaments should 3,107,972 Patented Get.22., 1963 2 first be conditioned in a high humidity (preferably steam)atmosphere to insure good package formation. For convenience, thisconditioning step has been accomplished as the filaments advance fromthe guide at which they were converged and arranged. If the undrawn yarnis not packaged but advanced directly to a draw zone, steam conditioningmay be omitted.

The above sequence of process steps produces a yarn which, onappropriate heating, e.g., in boiling water, develops a desirablebulkiness due to the higher denier filaments shrinking to a considerablygreater extent than the lower denier filaments. The bulkable yarn alsohas the advantage that there is no difference in retraction between thefilaments when the drawn yarn is removed from the package for processinginto fabric, i.e., it exhibits no troublesome loops of the type whichinterfere with such processing.

The shrinkage differentials disclosed herein are believed to arise froma higher degree of molecular orientation obtained when the filaments areseparated according to denier during the period when most of the undrawnfilament orientation occurs, i.e., after the filaments are properlyarranged by passage in contact with a guide. Conventionally, undrawnpolyamide filaments are brought in gliding contact after quenching witha solid surface such as a guide of the type normally used for convergingthe filaments into a single yarn end. If this is not done, substantiallyall of theattenuation of the filament takes place near the spinneretwhere the filament is quite plastic and little orientation occurs. Asdisclosed more fully hereinafter, the difference in orientation betweenthe low and relatively high denier filaments is insufficient to producethe desired differential shrinkability if the filaments are combined orgathered into a single bundle at the point of convergence. Althoughavoidance of contact between low and high deniers during attenuation isa requisite in the instant process, the filaments must be combined intoa single yarn end in advance of the draw zone in order to obtainsatisfactory drawing performance for all of the filaments.

In the following examples, the degree of orientation is determined bybirefringence measurements which involve observation of the undrawnfilaments between crossed plane-polarizing elements .(e.g., Nicolprisms) using a Soleil compensator for accuracy. This method is treatedin detail by Heyn in Textile Research Journal, 22, 513 (1952).

EXAMPLE I Polyhexamethylene adipamide having a relative viscosity of33.5 is prepared and extruded in the conventional manner using apparatusof the type disclosed in US. 2,217,743 except that the spinneret has 34holes varying in s ze as listed in Table I-A. The filaments are quenchedby passing air transversely across a chimney through which they travel.After quenching, the fourteen low denier filaments and the remainingtwenty filaments are converged into separate bundles by passing themseparately at a slight angle over matte finish, ceramic coated pins andthen over a second pin disposed at right angles to the first pins. Thetwo separate bundles are passed through a steam treatment enclosureprovided with entry and exit openings, steam inlets and a condensateoutlet. Steam is supplied to the enclosure at 5 p.s.i.g. and

the yarn is exposed to these turbulent conditions for a distance of 72inches. The two filament bundles are then gathered into a single yarnend which is packaged at a speed of 1560 yards/min. Subsequently, theyarn is unwound and drawn to a machine draw ratio of 3.2 by passing itaround spaced rolls, the second of which has a higher peripheral speed.Between these feed and draw rolls, the yarn is passed through anenclosure within which steam at p.s.i.g. and 275 C. is jetted on theyarn in an intersecting relationship. After drawing, the yarn is woundinto a package in a conventional manner. When exposed to boiling water,the cover and hand of the fabric are greatly improved due to thedifference in shrinkage between the low and higher denier filaments inthe yarn.

For purposes of comparison, samples of the packaged, undrawn filamentsare taken for birefringence measurements. The results of these tests areshown in Table I-A below. 1-11 additional tests, it is observed thatover 75% of the undrawn orientation, as indicated by birefringencemeasurements, occurs after the quenched filaments pass over theconvergence guide pins but within about 36 inches thereof. Beyond thispoint there is little change in orientation untii the filaments aredrawn.

Drawn yarn is separated into several bundles accord ing to denier tofacilitate the shrinkage determinations reported in the following table.It should be noted that the residual shrinkage in the one denierfilaments is less than 70% of the average residual shrinkage in theremaining filaments.

Table I-A Spinncret Filaments Number holes Diam Length, Bire- DenierPercent in in. h'ingence shrinkage Table I-B Number of Number of 1denier 2-4 denier Rating filaments filaments 1 Control, uniform d.p.i.

EXAMPLE II Filamentary yarn was prepared as in Example I except that itwas cold drawn over pins in the conventional manner and then steamedwhile permitting 9% relaxation, following the controlled relaxationprocedure described in U.S. 3,003,222. Table II shows shrinkages andundrawn filament birefringence values obtained when the quenched highand low denier filaments were converged separately as in Example Ibefore steam conditioning. Also shown in Table II, for comparison, areshninkages and birefringence values obtained when the quenched high andlow denier filaments were converged into a single yarn end beforeconditioning. It should be noted that the residual shrinkage in thelowest drawn denier filaments is less than of the average residualshrinkage in the remaining filaments when converged into two separatebundles but approaches when converged as a single bundle. As in ExampleI, it is found that birefringence of the undrawn filaments reaches amaximum within about 36 inches after passing over the convergenceguides.

The above examples illustrate the advantages of the instant process inwhich differential denier filaments are extruded from difierent holes ofthe same spinneret, quenched, separated according to denier in theirpassage over a guide, attenuated, gathered and subsequently drawn toproduce a non-loop filamentary yarn which is easily processed intofabric but which shrinks differentially when the fabric is heated, as inconventional fabric finishing operations, to produce a fabric withimproved cover and hand. The differences in filament shrinkage obtainedby this process are not so high as to produce a highly bulked yarn orfabrics having a cotton-like hand, but are sufiicient to bring the lowerdenier filaments to the surface of the fabric, thus producing a moderateincrease in bulk-iness and a soft luxurious hand which is highlydesirable.

As illustrated in the tables accompanying the examples, a particularcombination of process steps must be utilized to attain the desiredresults. The denier of the lower denier filaments should not be aboveabout 2, preferably not above 1.5, since the diiferences in shrinkageattained with variation in denier are greatest in the lower denierrange. In addition, the presence of such low denier filaments in thesurface of the fabric produces a soft hand. If desired, the low denierfilaments may vary in denier but their average denier should not begreater than 2. Likewise, the higher denier filaments may vary indenier, as exemplified, but their average denier should be at least 1.5times and preferably at least twice that of the lower denier filamentsin order to insure the desired shrinkage differential.

While, as shown in Table IB, a minor proportion of the lower denierfilaments will eifect a substantial imimprovement in fabric aesthetics,it is desirable that the lower denier filaments comprise a majornumerical proportion of the yarn.

The quenched, diiferential denier filaments must not be converged into asingle filament bundle at the usual point of convergence since,surprisingly, this results in a considerable loss in the shrinkagepotential of the low denier filaments, as best illustrated in Table II.Toobtain the desired shrinkage differential, the filaments must beseparated according to denier for a suificient distance after passing incontact with the guide to facilitate development of substantiallymaximum undrawn orientation. This is accomplished if the filaments arekept separated until the birefringence has substantially reached themaximum value for the undrawn filaments. Usually this will beaccomplished in a distance of 36 inches or less if a high humidityconditioning step is employed. If this step is omitted, a somewhatgreater distance may be required. The axial advance from the point ofconvergence and separation may also vary to some extent depending onfilament denier, spinning speed and other process variables. Separationmay be accomplished by guiding the filaments into two or more bundlesaccord ing to denier or, if convenient, the filaments may be spreadapart over a guide as a ribbon to avoid contact between low andrelatively high denier filaments. The latter must be combined into onebundle before drawing, otherwise the drawing performance of the lowerdenier filaments is not satisfactory. After the attenuated filamentshave been gathered, the resulting single yarn end may be passed directlyto the drawing stage or may be wound into a package ar-d drawnsubsequently.

The drawing step is preferably carried out in free space, -i.e., with nofrictional contact between the yarn and solid surfaces. As is apparentfrom a comparison of Tables LA and II, such space drawing provides thegreatest shrinkage difierence between the high and low denier filamentsand accordingly is the preferred procedure. Alternately, the gatheredfilamentary yann may be cold drawn over one or more pins, as in ExampleII, and then subjected to steam treatment with controlled relaxation asdescribed and claimed in US. 3,003,222. The steam treatment withrelaxation is necessary with pin drawn yarns to avoid loopiness due todifferences in the room temperature retraction of the filaments when thedrawn yarn is unwound from its package.

The preferred polyamides for use in the process of this invention arepoly(hexamethylene adiparnide) and poly(epsilon caproamide). Othersuitable polyamides include those described in U.S. Patents 2,071,253;2,130,- 523 and 2,130,948.

Having thus described the invention, what is claimed as new and desiredto be secured :by Letters Patent is:

1. In the production of yarn, the steps of: guiding freshly spun,axially advancing, differential denier, polyamide filaments into bundlesaccording to denier; and gathering said bundles, after their axialadvance under tension through a distance sufiicient to developsubstantially maximum undrawn orientation, into a single yarn endadapted to be drawn to a denier of less than 2 for the filaments fromone or" said bundles and a denier at least 1.5 times as great for theremaining filaments.

2. In the production of yarn, the steps of: guiding freshly spun,axially advancing, differential denier, polyamide filaments intoseparate bundles according to denier; gathering said separate bundles,after their axial advance under tension through a distance sufiicient todevelop substantially maximum undrawn orientation, into a single yarnend; and drawing said yarn end, the filaments from one of said bundleshaving a drawn denier of less than 2, the remaining filaments having adrawn denier at least 1.5 times as great.

3. In the production of yarn, the steps of: spinning low and relativelyhigh denier filaments from a molten polyamide; quenching the spunfilaments; separating the quenched filaments, by passage in contact withguide means, into bundles according to denier; conditioning said bundlesby exposure to an atmosphere having a relative humidity of at least 90%and a temperature of at least 65 C.; and gathering said bundles, aftertheir axial advance under tension through said atmosphere and through afurther distance sufficient to develop substantially maximum undrawnorientation, into a single yarn end adapted to be drawn to a denier ofless than 2 for the filaments from one of said bundles and a denier atleast 1.5 times as great for the remaining filaments.

4. A process including the steps of spinning, quenching and drawingdifferential denier nylon yarn containing a major numerical proportionof filaments having a drawn denier of less than 1.5, the improvement ofwhich comprises guiding the quenched filaments into low and relativelyhigh denier bundles and, in advance of said drawing step but after theiraxial advance under tension through a distance suificient to developsubstantially maximum undrawn orientation, gathering the bundles into asingle yarn end.

5. The process of claim 4 wherein :said yarn end is cold drawn bysnubbing contact with an element situated in the yarn path of travelbetween spaced feed and draw rolls and subsequently relaxed in a steamatmosphere.

6. in the production of yarn, the steps of: spinning low and relativelyhigh denier polyamide filaments; arranging the axially advancingfilaments to avoid contact between low and high denier filaments; andgathering the filaments, after an axial advmce from the point ofarrangement through a distance .sufiicient to develop substantiallymaximum undrawn orientation, into a bundle adapted to be drawn to adenier of less than 2 for the low denier filaments and a denier at least1.5 times as great for the remaining filaments.

7. A process including the steps of spinning, quenching and drawingdifferential denier nylon yarn containing a major numerical proportionof filaments having a drawn denier of less than 1.5, the improvement ofwhich comprises arranging the quenched filaments to avoid contactbetween those in said major porportion and those remaining and gatheringthe arranged filaments, in advance of said drawing step but after anaxial travel from the point of arrangement through a distance suificientto develop substantially maximum undrawn orientation, into a single yarnend.

8. In the production of yarn, the steps of: guiding as-spun, axiallyadvancing, differential denier, nylon filaments to avoid contact betweenlow and relatively high denier filaments; gathering the filaments, aftera guided advance through a distance sufi'icient to develop maximumundrawn orientation, into a single yarn end; and drawing said yarn end.

References Cited in the file of this patent UNITED STATES PATENTS2,273,106 Heckert Feb. 17, 1942 2,851,732 Sharp Sept. 16, 1958 2,990,236Riseley June 27, 1961 3,038,779 Hechler et al. June 12, 1962 I FOREIGNPATENTS 495,734 France May 31, 1950 132,369 Sweden July 17, 1951

1. IN THE PRODUCTION OF YARN, THE STEPS OF: GUIDING FRESHLY SPUN,AXIALLY ADVANCING, DIFFERENTIAL DENIER, POLYAMIDE FILAMENTS INTO BUNDLESACCORDING TO DENIER; AND GATHERING SAID BUNDLES, AFTER THEIR AXIALADVANCE UNDER TENSION THROUGH A DISTANCE SUFFICIENT TO DEVELOPSUBSTANTIALLY MAXIMUM UNDRAWN ORIENTATION, INTO A SINGLE YARN ENDADAPTED TO BE DRAWN TO A DENIER OF LESS THAN 2 FOR THE FILAMENTS FROMONE OF SAID BUNDLES AND A DENIER AT LEAST 1.5 TIMES AS GREAT FOR THEREMAINING FILAMENTS.